1. Field of the Invention
The present invention relates to a stator for a generator-motor and a method for producing the stator.
2. Description of the Related Art
A stator as disclosed in JP-A-2000-156943 is known in the related art. In the stator, a stator iron core is separated into teeth iron core portions and core back iron core portions. After a stator winding is put in slot portions between the teeth iron core portions, the core back iron core portions are inserted in between the teeth iron core portions from the radially outer, side of the stator.
In such a stator, there is known a method in which a wire bundle constituted by a bundle of a plurality of electric wires is provided to make several revolutions so that the wire bundle weaves through the teeth iron core portions when the stator winding is put in the slot portions between the teeth iron core portions.
In the stator according to the related art, however, when, for example, a plurality of wire bundles are provided to come full circle to thereby form a stator winding, the wiring length of a wire bundle on an outer circumferential side between the teeth iron core portions becomes larger than the wiring length of a wire bundle on an inner circumferential side between the teeth iron core portions. Hence, the difference between the wiring lengths causes a difference between resistance values. For this reason, if a predetermined voltage is applied to the stator winding, a larger current flows in a wire bundle provided on an inner circumferential side and having a relatively smaller resistance value among the plurality of wire bundles connected in parallel with one another. As a result, the amount of heat generated in the wire bundle increases.
Here, a predetermined temperature up to which the stator winding exhibits heat resistance (hereinafter referred to as “heat-resistant temperature”) is set in the stator winding. A predetermined allowable electric power supply range for an electric source or the like is determined so that the temperature of the stator winding can change in a predetermined temperature range corresponding to the heat-resistant temperature. There is, however, a possibility that it may be difficult to make various current conduction control by effectively utilizing the heat-resisting performance of the stator winding because the predetermined temperature range for the stator winding, that is, the allowable electric power supply range, is narrowed when the amount of heat generated in the wire bundle varies largely.
When, for example, the ratio of the resistance value change to the temperature change due to heat generation is 0.4%/° C. and the difference between resistance values of wire bundles is 14.3%, a temperature difference of 14.3/0.4≈36° C. is generated locally in the stator winding. Assuming now that the atmospheric temperature of the stator winding is 80° C. and the heat-resistant temperature is 180° C., then the predetermined temperature range for the stator winding, that is, the allowable electric power supply range is 180−80=100° C. There is, however, a possibility that the temperature range may be narrowed to 100−36=64° C. if a temperature difference of 36° C. is generated locally.
If such a temperature difference is generated when the temperature of the stator winding is a value near the predetermined heat-resistant temperature (for example, 180° C.), there is a possibility that the temperature of the stator winding may exceed the heat-resistant temperature because the temperature of the stator winding reaches 180+36=216° C. locally.
As measures against the problem, two methods are known in the case where a predetermined number of electric wires (for example, 80 electric wires) are connected in parallel with one another and provided to make several rounds (for example, three rounds) to thereby form a stator winding. The first method is a method in which the plurality of electric wires are connected in parallel with one another to thereby form one wire bundle and in which the wire bundle is provided to make several rounds. The second method is a method in which the plurality of electric wires are separated into a plurality of wire bundles (for example, four wire bundles) by a predetermined number of electric wires (for example, 20 electric wires) and in which the wire bundles are connected in parallel with one another after each of the wire bundles is provided to make several rounds (for example, three rounds).
In the first method, when one wire bundle is provided to make several rounds, the wire bundle is twisted at each predetermined position to transfer the inner circumferential side of the wire bundle to the outer circumferential side to thereby equalize the wiring lengths of electric wires constituting the wire bundle.
In this stator winding, there is, however, a possibility that the space factor may be lowered because a gap is produced between adjacent parts of the wire bundle, for example, in the position where the wire bundle is twisted.
In the second method, after each of the wire bundles is provided to make several rounds, a setting is made so that the length of a lead wire from each of the wire bundles is adjusted to a predetermined value and the wire bundles are connected in parallel with one another to thereby equalize the wiring lengths of the wire bundles inclusive of the lengths of the lead wires to one another. When, for example, the length of a lead wire from a wire bundle disposed on the outer circumferential side between the teeth iron core portions is set to be smaller than the length of a lead wire from a wire bundle disposed on the inner circumferential side between the teeth iron core portions, the difference between resistance values can be prevented from being caused by the difference between the wiring lengths of the wire bundles.
In such a stator winding, however, the length of the lead wire for the wire bundle disposed on the inner circumferential side needs to be made longer than other wires in order to increase the resistance value. As such, there is a possibility that the cost for production of the stator winding may increase. Moreover, because the lead wire becomes long, the coil end height becomes high. As such, there is a possibility that the size of the stator may increase.
The present invention is designed upon such circumstances and an object of the invention is to provide a stator in which the temperature difference in winding temperature between a plurality of electric wires constituting a stator winding can be suppressed while the size and production cost of the stator can be prevented from increasing, and to provide a method for producing the stator.